Metal ions play essential roles in diverse physiological processes in insects, including immunity and interactions with microbes. Some, like iron, are essential nutrients and therefore are the subject of a tug-of-war between insects and microbes. Recent findings showed that the hypoferremic response mediated by Transferrin 1 is an essential defense mechanism against pathogens in insects. Lately, Transferrin 1 and the overall iron metabolism were also implicated in mediating interactions between insects and beneficial microbes. Other metals, like copper, can interfere with insect immune effectors, and either enhance (antimicrobial peptides) or reduce (reactive oxygen species) their activity.
Heavy metals are one of the important factors of environmental pollution to which insects are exposed to. Heavy metals can interfere with numerous host physiological processes, including immune responses. Several recent studies, using different insects, reported that exposure to heavy metals reduced the numbers of hemocytes, thus impairing the cellular immune response.
Upregulation of the detoxification and antioxidant enzymes in insects exposed to heavy metals was observed in several cases, sometimes resulting in increased susceptibility to infection as a result of a trade-off between detoxification and immunity.
The transgenerational effect of heavy metal exposure on immune response was also reported in the Blow Fly Protophormia terraenovae. Such negative effects of heavy metal exposures on insect physiology and immunity in particular raise concerns regarding the use of insect meals in animal feed, particularly in aquaculture.